JP4532560B2 - De-jitter buffer adjustment based on estimated delay - Google Patents

Description

  Embodiments disclosed herein generally relate to communication, and more particularly, to adaptively managing packet jitter in a packet-switched wireless communication system.

  In a packet switched network, the sending computer breaks the message into a series of small packets and labels each packet with an address that tells the network where to send it. Each packet is then routed to its destination via the most convenient route available. This means that not all packets traveling between the same two communication systems need to follow the same path, even if they are packets from a single message. When the receiving computer receives the packet, it reconstructs the packet into the original message.

  Because each packet is handled separately, it incurs a specific amount of delay that is different from the delay time experienced by other packets in the same message. This change in delay, known as “jitter”, adds additional complexity to the receiving application due to packet delay times when reconstructing messages from received packets. If the jitter is not corrected, the received message will be distorted if the packet is reassembled.

  Unfortunately, in VoIP systems operating over the Internet, there is no information available that can be used by a de-jitter buffer to predict changes in packet delay, and the de-jitter buffer adapts to predict such changes. I can't do it. Instead, the de-jitter buffer typically has to wait for the arrival of a packet in order to detect changes in packet delay by analysis of packet arrival statistics. Thus, the de-jitter buffer is passive and adjusts only after packet delay changes have occurred. Many de-jitter buffers cannot change at all and are simply configured to be conservatively large in size. This adds unnecessary delay to message playback, as described above, and makes the user experience suboptimal. Therefore, there is a need in the art for adaptive delay management to efficiently remove jitter from packet transmissions in a communication system with changing channels.

  One aspect of the present invention is a method for adapting a de-jitter buffer, the method detecting an air link characteristic, estimating a packet delay based on the characteristic, and estimating the estimated Adapting the de-jitter buffer based on the packet delay.

  Another aspect of the invention is a method for adapting a de-jitter buffer prior to a handoff event, the method comprising scheduling the handoff event and packet delay based on the scheduled handoff event. Estimating and adapting the de-jitter buffer based on the estimated packet delay.

  Another aspect of the present invention is a method for initializing a de-jitter buffer, the method comprising: detecting a characteristic of an air link; estimating a packet delay based on the characteristic; and Initializing the jitter buffer based on the packet delay.

  In another aspect of the present invention, the subscriber station acquires an antenna configured to receive a communication signal through a wireless air link, a measurement value of the air link characteristic, and a function of the acquired air link characteristic. And a processor configured to calculate a de-jitter buffer size and a de-jitter buffer configured to have an adaptable size that can match the calculated size.

  In a further aspect of the invention, the subscriber station obtains information about the scheduled handoff and estimates a packet delay as a function of the scheduled handoff, and a demodulator as a function of the estimated packet delay. A processor configured to calculate a jitter buffer size and a de-jitter buffer configured to have an adaptable size that can be matched to the calculated size.

  In yet a further aspect of the invention, a computer readable medium includes a program comprising computer executable instructions for performing a method of adapting a de-jitter buffer. The method includes detecting air link characteristics, estimating packet delay based on the characteristics, and adapting the de-jitter buffer based on the estimated packet delay.

  Another aspect of the invention includes a program comprising computer-executable instructions for performing a method in which a computer-readable medium adapts a de-jitter buffer prior to a handoff event. The method includes scheduling the handoff event, estimating a packet delay based on the scheduled handoff event, and adapting the de-jitter buffer based on the estimated packet delay. .

  In yet another aspect of the invention, the subscriber station is configured to receive a communication signal over a wireless air link, to calculate a de-jitter buffer size as a function of the received air link characteristic, and to calculate the calculated Means for adapting the size of the de-jitter buffer such that the de-jitter buffer matches the size.

  In a further aspect of the invention, the subscriber station is configured to obtain information regarding scheduled handoffs, means for estimating packet delay as a function of the scheduled handoff, and as a function of the estimated packet delay. Means for calculating a de-jitter buffer size and means for matching the de-jitter buffer to the calculated size.

  Circuit switching has been used by telephone line networks for over 100 years. When a call is made between two parties, the connection is maintained for the entire duration of the call. However, much of the data transmitted during that time is wasted. For example, while one is speaking, the other is listening and only half of the connection is used. In addition, most of the time in many conversations includes silent time when neither is speaking. Thus, circuit switched networks actually waste available bandwidth by sending unnecessary communication data over continuously open connections.

  Instead of passing data through circuit-switched networks all the time, many data networks (such as the Internet) generally use a method known as packet switching. Packet switching opens a connection between two communication systems of just the right length to send a small chunk of data called a “packet” from one system to another. These short connections are not maintained if they are repeatedly opened for passing data packets but no data is sent. In a packet switched network, the sending computer breaks the message into a series of small packets and labels each packet with an address that tells the network where to send it. Each packet is then routed to its destination via the most convenient route available. This means that not all packets traveling between the same two communication systems need to follow the same path, even if they are packets from a single message. When the receiving computer receives the packet, it reconstructs the packet into the original message.

  Circuit switched voice communications are emulated on a packet switched network. IP telephony, known as Voice over IP (VoIP), uses packet switching for voice communication and provides several advantages over circuit switching. For example, the bandwidth savings provided by packet switching allows several telephone calls to occupy the amount of network space (bandwidth) occupied by only one telephone call in a circuit switched network. However, VoIP is known to be a delay sensitive application. Since a transmitted message cannot be heard by the recipient until at least a certain amount of packets have been received and reassembled, the delay in the received packet will cause the transmission rate of the entire message and the transmitted message to be timely. May adversely affect the ability of the receiving communication system to rebuild.

  Delays in packet transmission can be caused, for example, by complex operating systems that use processing time required to packetize communication data, hardware and software delays during packet processing, and time-consuming methods for packet dispatch. Is caused. In addition, the communication network itself may introduce a delay in packet delivery time. The inconvenience caused by such delays is increased by the fact that in a packet switched system, each packet experiences a different amount of delay time. Because each packet is handled separately, it incurs a specific amount of delay that is different from the delay time experienced by other packets in the same message. This change in delay, known as “jitter”, adds further complexity to receiver-side applications that must consider packet delay times when reconstructing messages from received packets. If the jitter is not corrected, the received message will be distorted if the packet is reassembled.

  One method that attempts to reduce the effects of jitter in packet transmission involves using a de-jitter buffer. In general, the de-jitter buffer removes delay changes by adding further delay at the receiver side. By implementing this delay time, the de-jitter buffer can be queued in the holding area when a packet arrives. Packets arriving at the de-jitter buffer may arrive at inconsistent times, but these packets are acquired by the receiver processor at consistent timing. The processor simply gets the packet from the queue in the de-jitter buffer when needed. Therefore, the de-jitter buffer can perform packet acquisition smoothly by adding a certain amount of additional delay to the packet arrival time.

  As an example, for digital voice communications, a continuous flow of information typically includes voice packets every 20 milliseconds. A de-jitter buffer is not necessary if the persistent channel can deliver packets every 20 milliseconds. This is because the receiver is already accessing packets at a consistent 20 ms arrival rate. However, in the case of a variable channel that delivers packets at an inconsistent rate due to processing delays, etc., de-jitter requires that the receiver side smooth the packet rate. In general, the additional delay added by such a de-jitter buffer is set to the longest running length with no packet arrival during transmission. For example, if the transmission includes 80 ms execution between packet arrivals and this is an execution without the longest packet, the de-jitter buffer is at least 80 ms in size to accommodate the gap. Should. However, such a large de-jitter buffer would not be necessary for a variable channel with an execution without the longest packet of 40 milliseconds. In this case, the 80 millisecond de-jitter buffer would simply implement an unnecessary 40 millisecond delay in the communication flow. Alternatively, the de-jitter buffer would only need to be 40 milliseconds in size.

  Wireless communication systems are diverse and often include invariant channels, variable channels, and highly variable channels. Thus, a large de-jitter buffer that works well with highly variable channels is over-equipped for an invariant channel that does not require a de-jitter buffer. However, if the de-jitter buffer is too small, it will not be possible to filter the jitter in the highly variable channel. Also, a small de-jitter buffer may lose some packets (to catch up with packet playback) when a large burst of packets arrives, and a long transmission is in progress while no packets arrive , Packets may decrease.

  Unfortunately, in VoIP systems operating on the Internet, there is no information that the de-jitter buffer can use to predict changes in packet delay, and the de-jitter buffer cannot adapt to predict such changes. Instead, the de-jitter buffer typically must wait for the arrival of a packet in order to detect changes in packet delay by analyzing packet arrival statistics. Thus, the de-jitter buffer is passive and adjusts only after packet delay changes have occurred. Many de-jitter buffers cannot change at all and are simply configured to be conservatively large in size. This adds unnecessary delay to message playback, as described above, and makes the user experience suboptimal. Accordingly, there is a need in the art for adaptive delay management to efficiently remove jitter from packet transmissions in a communication system having a variable channel.

  FIG. 1 illustrates a wireless communication system 100 that supports multiple users and is capable of implementing at least some aspects and embodiments of the present disclosure. The communication system 100 provides a communication function to a plurality of cells 102A to 102G. Each of the cells is served by a corresponding base station 104A-104G. In the exemplary embodiment, some of the base stations 104 have multiple receive antennas and others have only one receive antenna. Similarly, some of the base stations 104 have multiple transmit antennas and others have a single transmit antenna. There is no limitation on the combination of the transmitting antenna and the receiving antenna. Therefore, whether the base station 104 has multiple transmission antennas and a single reception antenna, multiple reception antennas and a single transmission antenna, both the multiple transmission antennas and reception antennas, or both It is possible to have a single transmit antenna and receive antenna. Multiple users may access communication system 100 using individual subscriber stations 106A-106J. As used herein, the term “subscriber station” refers to a car phone, cellular phone, satellite phone, personal digital assistant, or any other remote station or wireless communication device.

  The illustrated wireless communication system 100 uses, for example, code division multiple access (CDMA) technology. A CDMA communication system is a modulation and multiple access scheme based on spread spectrum communication. In a CDMA communication system, many signals share the same frequency spectrum, resulting in increased user capacity. This is accomplished by transmitting each signal with a different quasi-random binary sequence that modulates the carrier. This spreads the spectrum of the signal waveform. The transmitted signals are separated in the receiver by a correlator that despreads the spectrum of the desired signal using the corresponding quasi-random binary sequence. Undesired signals whose quasi-random binary sequences do not match are not despread in bandwidth and contribute only to noise.

  More particularly, CDMA systems allow voice and data communication between users over terrestrial links. In a CDMA system, communication between users is routed through one or more base stations. In wireless communications, “forward link” refers to the channel through which the signal travels from the base station to the subscriber station, and “reverse link” refers to the channel through which the signal travels from the subscriber station to the base station. By transmitting data on the reverse link to the base station, the first user of the first subscriber station communicates with the second user of the second subscriber station. The base station receives data from the first subscriber station and routes this data to the base station serving the second subscriber station. Depending on the location of the subscriber station, the subscriber station can be served by a single base station or by both multiple base stations. In any case, the base station serving the second subscriber station can send data on the forward link. Instead of communicating with a second subscriber station, the first subscriber station may also communicate using the terrestrial Internet via a connection with a serving base station.

  As will be appreciated by those skilled in the art, a CDMA system may be designed to support one or more standards, for example: (1) "TIA / EIA / IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" referred to as IS-95 standard in this specification, (2) W- in this specification Proposed by a consortium named “3rd Generation Partnership Project”, referred to as the CDMA standard and referred to herein as 3GPP, document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, 3G TS 25.214, and 3G TS 25.302 (3) formerly referred to as IS-2000MC, referred to herein as cdma2000, referred to herein as 3GPPS and TR-45.4, "3rd Generation Partnership Project" A standard proposed by a consortium named 2 ", or (4) some other radio standard.

  The increasing demand for wireless data transmission and the expansion of services available through wireless communication technology has led to the development of concrete data services. One such service is called high data rate (HDR). Such an HDR service is proposed in, for example, “EIA / TIA-IS856 cdma2000 High Rate Packet Data Air Interface Specification” called “HDR specification”. An HDR service is generally an overlay to a voice communication system that provides an efficient way to transmit packets of data in a wireless communication system. As the amount of data transmitted and the number of transmissions increase, the limited bandwidth available for radio transmission becomes a critical resource.

  One example of a communication system that supports HDR services is referred to as 1xEvolution Data Optimized ("1xEV / DO"). 1xEV-DO has been standardized by the Telecommunications Industry Association as TIA / EIA / IS-856, “cdma2000, High Rate Packet Data Air Interface Specification” (cdma2000, High Rate Packet Data Air Interface Specification). 1xEV-DO is optimized for high performance and low cost packet data services, bringing personal wireless broadband services to a wide range of users. The teachings herein are applicable not only to 1xEV-DO systems, but also to other types of HDR systems, including but not limited to W-CDMA and 1xRTT. It should also be understood that the teachings herein are not limited to CDMA systems but are equally applicable to orthogonal frequency division multiplexing (OFDM) and other radio technologies and interfaces.

  An HDR communication system applying a variable rate data request scheme is shown in FIG. The HDR communication system 200 may include a CDMA communication system designed to transmit at high data rates, such as 1xEV-DO or other types of HDR communication systems. The HDR communication system 200 may include a subscriber station 202 that communicates with the ground-based data network 204 by transmitting data on the reverse link to the base station 206.

Base station 206 receives the data and routes the data to ground-based network 204 via base station controller (BSC) 208. Conversely, communications to the subscriber station 202 are routed from the ground-based network 204 via the BSC 208 to the base station 206 and transmitted from the base station 206 to the subscriber unit 202 on the forward link. One skilled in the art will appreciate that forward link transmissions can occur between the base station 206 and one or more subscriber stations 202 (multiple not shown). Similarly, reverse link transmissions can occur between one subscriber station 202 and one or more base stations 206 (multiple not shown).

  In the exemplary HDR communication system, forward link data transmission from base station 206 to subscriber station 202 may occur at the maximum or approximately maximum data rate supported by the forward link. Initially, subscriber station 202 may establish communication with base station 206 using a predetermined access procedure. In this connected state, the subscriber station 202 can receive data and control messages from the base station 206 and can transmit this data and control messages to the base station 206.

  Once connected, the subscriber station 202 can estimate the carrier-to-interference ratio (C / I) of the forward link transmission from the base station 206. The C / I for forward link transmission can be obtained by measuring the pilot signal from the base station 206. Based on this C / I estimation, the subscriber station 202 can transmit a data request message (DRC message) to the base station 206 on a data request channel (DRC channel). The DRC message contains the required data rate or the quality indication of the forward link channel, eg C / I measurement itself, bit error rate or packet error rate, from which the appropriate data rate Can be identified. Alternatively, subscriber station 202 continuously monitors the channel quality and calculates the data rate at which subscriber station 202 can receive the next data packet transmission. In any case, base station 206 uses DRC messages from subscriber stations to efficiently transmit forward link data at the highest possible rate.

  FIG. 3 is a block diagram illustrating a basic subsystem of a typical HDR communication system 300. The BSC 302 interfaces with the packet network interface 304, the PSTN 306, and all base stations in a typical HDR communication system (only one RF unit 308 is shown for simplicity). The RF unit 308 can transmit communication data to the subscriber station via the antenna 310 under the control of the BSC 302. The BSC 302 may coordinate communication between multiple subscriber stations in a typical HDR communication system and other users connected to the packet network interface 304 and the PSTN 306. The PSTN 306 may interface with the user via a standard telephone network (not shown).

  Data source 314 may include data to be transmitted to the target subscriber station. Data source 314 may provide data to packet network interface 304. The packet network interface 304 receives the data and routes them to the BSC 302. The BSC 302 then sends the data to the RF unit 308 that is in communication with the target subscriber station. The RF unit 308 then inserts a control field into each data packet. This results in a formatted packet. The RF unit 308 encodes the formatted data packet and interleaves (re-adjusts) the symbols in the encoded packet. Next, each interleaved packet is scrambled with a scrambling sequence and covered with a Walsh cover. This scrambled data packet is then punctured to accommodate the pilot signal and power control bits and spread with a long PN code, a short PNI and a PNQ code. The spread data packet is quadrature modulated, filtered and amplified. Those skilled in the art will appreciate that other signal processing methods are implemented as well, and the teachings herein are not limited to the specific processing steps described above. After processing, the forward link signal may be transmitted over the forward link to the target subscriber station via air via antenna 310. A data sink 316 is provided for receiving data and storing the received data.

  The hardware described above supports variable rate transmission of data, messages, voice, video, and other communications over the forward link. Both forward link and reverse link data rates may vary to accommodate changes in signal strength and noise environment at the subscriber station. Such changes can result in packet delay changes, ie jitter. For example, the RF unit 308 may control the transmission rate of the subscriber station with reverse activity (RA) bits. The RA bit is a signal sent from the base station to the subscriber station and indicates how much the reverse link is loaded (ie, how much data is being sent on the reverse link). If the subscriber station has more than one base station in its active set, the subscriber station may receive RA bits from each base station. The term “active set” as used herein refers to a base station with which a subscriber station communicates. The received RA bit may indicate whether the total reverse traffic channel interference is above a certain value. This will then indicate whether the subscriber station will increase or decrease its data rate on the reverse link. Similarly, the traffic channel valid (TCV) bit is a signal sent from the base station to the subscriber station and indicates how many users are in the sector. The TCV bit does not accurately indicate how heavily the forward link is loaded, but may be somewhat related to sector loading. Thus, the TCV bit may indicate whether the subscriber station can increase or decrease the data rate requirement for transmission on the forward link. In either case, a change in data rate can cause a change in packet delay, ie jitter.

  The data transmission rate can also be adjusted by other signal quality indications. As described above, signal quality in communication is determined by measuring the C / I of the channel. One skilled in the art will appreciate that other methods of determining channel quality can be used as well. For example, signal-to-interference and noise ratio (SINR) or bit error rate (BER) are measurable characteristics that indicate signal quality. If a change in signal quality is detected, the transmission may be increased or decreased accordingly. Such changes may also result in packet jitter.

  In addition to affecting the data transmission rate, signal quality measurements may cause an event known as “handoff”. For example, when a subscriber station moves from a first location to a second location, the channel quality may decrease. However, the subscriber station may be able to establish a higher quality connection with the base station close to the second location. Thus, a soft handoff procedure may be initiated to transfer communication from one base station to another. Soft handoff is the process of selecting another sector where data is sent to the subscriber station. After a new sector is selected, an air traffic link is established with the new base station (in the selected sector) before breaking the existing air traffic link with the original base station. This approach not only reduces the probability of a lost call, but also makes the handoff virtually undetectable to the user.

  Soft handoff is when the subscriber station approaches the second location, detects an increase in pilot signal strength from the second base station, and reports this information to the BSC via the first base station. Started by. The second base station is then added to the subscriber station's active set and an air traffic link is established. The BSC then deletes the first base station from the active set and tears down the air traffic link between the subscriber station and the first base station.

  Accordingly, various indications of signal quality are used to adjust the packet transmission rate over both the forward and reverse links in a wireless communication system. However, as noted above, such changes may also affect packet delay at the subscriber station. Accordingly, the de-jitter buffer is configured to have an adaptable size. This allows adaptation to such changes before they occur.

  FIG. 4 illustrates a subscriber station 400 configured to receive communication data formatted and transmitted as described above in connection with FIG. At target subscriber station 400, forward link signal 402 may be received by antenna 404 and routed to front end receiver 406. The front-end receiver 406 performs signal filtering, amplification, quadrature modulation, and quantization. This digitized signal is supplied to a demodulator (DEMOD) 408, where it is despread using short PNI and PNQ codes and decovered with a Walsh cover. This demodulated data is supplied to the decoder 410 where the inverse of the signal processing function performed by the base station 208, specifically, the deinterleaving, decoding, and CRC checking functions are performed. In the subscriber station 400, other signal processing configurations can be implemented. It should be understood that the specific functions identified above are for illustrative purposes only. In general, the processing at subscriber station 400 may operate in accord with signal processing caused at the base station. In any case, after processing, the decoded data can be provided to the data sink 414 of the subscriber station 400.

  Prior to provision to data sink 414, this decoded data can be held in de-jitter buffer 412. De-jitter buffer 412 may add a certain amount of delay to each data packet. In addition, the de-jitter buffer may add another amount of delay to another data packet. Thus, if an increase in jitter is expected, the de-jitter buffer will increase in size to add a longer delay time, and if a decrease in jitter is expected, the de-jitter buffer will add a shorter delay time. To reduce the size. To do so, the de-jitter buffer can be configured to have an adaptive size.

  The de-jitter buffer can adapt its size through a process called “time warp”. Time warp is the process of compressing or expanding a speech frame, such as a packet, in a de-jitter buffer as described herein. For example, if the dejitter buffer begins to deplete, the time warp extends the packet as it is obtained from the dejitter buffer by an application operating at the subscriber station. If the de-jitter buffer becomes larger than the currently calculated de-jitter buffer size, the time warp compresses the acquired packet.

  The compression and expansion of data packets is likened to increasing or decreasing of packets at a rate obtained at the subscriber station in relation to the arrival rate. For example, if a packet arrives and enters the de-jitter buffer once every 20 milliseconds, but is acquired once every 40 milliseconds, this is expanded. This effectively increases the size of the de-jitter buffer and receives twice as many packets to transmit. Similarly, if a packet arrives and enters the de-jitter buffer once every 20 milliseconds, but is acquired once every 10 milliseconds, it is compressed. This effectively reduces the size of the de-jitter buffer and receives half of the packets to transmit. This amount of extension applied to the packets in the de-jitter buffer can be, for example, 50-75% (ie, 20 ms to 30-35 ms). This amount of compression applied to the packets in the de-jitter buffer may be, for example, 25% (ie 20 to 15 milliseconds). While these compression rates may prevent severe degradation of voice quality, those skilled in the art will appreciate that other rates can be used effectively.

  A processor 416 that communicates with the de-jitter buffer may calculate the amount of delay (ie, the size of the de-jitter buffer) as a function of air link characteristics. These characteristics are measured by the subscriber station 400 and used by the processor 416 to calculate the appropriate de-jitter buffer size as will be described in more detail.

  In a wireless communication system, some measurable information can be highly correlated with the packet jitter experienced at the subscriber station. For example, as described above, it is the air interface used in the communication system that contributes decisively to changes in packet delivery delay. In particular, in 1xEV-DO systems, sector load is correlated to end-to-end message delay and packet jitter. The sector load can be estimated based on, for example, RA bits or TCV bits. Signal quality is also correlated to packet jitter. For example, average sector signal quality correlates with end-to-end message delay, while changes in sector signal quality correlate with packet jitter. Furthermore, handoff between base stations is correlated to jitter. Based on these relationships, the de-jitter buffer 412 disclosed herein adaptively provides high performance. De-jitter buffer size adaptation can occur, for example, at initialization, during steady state operation, and during handoff.

  Sector loading, signal quality, and signal quality changes can be used as inputs to the de-jitter buffer to improve operation during initialization. As already explained, a de-jitter buffer is generally initially set at a conservative value to ensure that sufficient delay is added to the incoming packet even before the exact degree of jitter is determined. It becomes. In the exemplary de-jitter buffer 412 disclosed herein, other information on packet arrival statistics included in the packet may be used as input to determine a realistic value for initialization. For example, if the sector load is low, the signal quality received at the subscriber station is high, and the change in signal quality is low, the subscriber station 400 may be stationary and / or in a good reception area. Can be considered. In such a preferred situation, jitter is estimated to be small and the de-jitter buffer can be configured to have a small size. As described above, the sector load can be determined by the RA bit or the TCV bit. These bits can be received from the base station via antenna 404 and interpreted by processor 416. Processor 416 may then instruct dejitter buffer 412 to adapt accordingly. Thus, the illustrated de-jitter buffer need not be initialized with a conservative and unnecessarily long delay value. In the case of VoIP, the low initial value for the de-jitter buffer changes to a small delay at the beginning of the user's VoIP call, which is an improved service for the user.

  After initialization, for example, during steady state operation, the signal quality within a sector may be used to improve de-jitter buffer operation. Changes in signal quality may be detected by the subscriber station even before these changes begin to affect packet arrival times. Thus, signal quality measurements are made to detect these changes, and these measurements can be used to adjust the de-jitter buffer size before the affected packet begins to arrive.

  In order to detect changes in signal quality, sector signal quality can be measured over time. By maintaining a running average, changes in signal quality and average signal quality over time can be calculated. Thus, both positive and negative changes in signal quality are identified and analyzed by the processor 416. The processor 416 can also make appropriate adaptations of the de-jitter buffer 412. For example, a sector signal quality change can indicate an impending change in packet delay, thus triggering a de-jitter buffer that adapts its size for a new delay time.

  In one embodiment, the filter may be used to track signal quality running averages. Short-term averages can be compared to detect changes in sector signal quality. One example of a filter that can be used is a 64 slot filter with a slot length of 1.66 milliseconds. This would be a short term average of approximately 20 milliseconds. One skilled in the art will recognize that other filters can be used as well. By comparing the continuous values in the running average measurement, the subscriber station can detect changes in the sector signal quality. If the signal quality change indicates a negative change, an increased packet delay is expected and the processor 416 may instruct the de-jitter buffer 412 to increase the size in preparation for this delay. On the other hand, if a change from low signal quality to high signal quality is detected, a decrease in packet delay is expected and de-jitter buffer 412 may reduce its size.

  In addition to initialization and steady state operation, the de-jitter buffer disclosed herein can accommodate and anticipate handoff events. Preliminary information regarding planned or scheduled handoffs that may be generated by the subscriber station 400 may be used to trigger the dejitter buffer 412 to adapt prior to the actual handoff event. Handoff may be the largest source of sudden and extreme packet jitter in 1xEV-DO systems and other wireless systems. Handoff events are triggered by the subscriber station and they are generally scheduled a few milliseconds before execution. In 1xEV-DO, for example, a handoff may be scheduled more than 100 milliseconds before its execution. In the exemplary embodiment disclosed herein, scheduling information is provided to de-jitter buffer 412, which can be adapted prior to handoff.

  Subscriber station 400 may include a sector selection algorithm that monitors the strength of the pilot signal as subscriber station 400 moves relative to various base stations. If the pilot signal from the connected base station is sufficiently reduced and a handoff to a new base station is required, the sector selection algorithm will inform the connected base station of the scheduled handoff. A signal sent to the base station may be generated. In one embodiment, this signal is also sent to processor 416 or de-jitter buffer 412. This signal may trigger dejitter buffer 412 to increase its size in preparation for a handoff that is likely to occur. Alternatively, a sector selection algorithm implemented by a processor, such as processor 416, may send a signal directly to de-jitter buffer 412 at the same time or nearly the same time as the signal is sent to the connected base station. This will allow the de-jitter buffer 412 to adjust for a longer time before the handoff event occurs. After the handoff is complete, the sector selection algorithm signals to the de-jitter buffer 412. This triggers the de-jitter buffer 412 to resume normal operation.

  FIG. 5 illustrates a method for adaptively adjusting the de-jitter buffer. This enhances its performance according to the characteristics of the air interface being used. Any part of the method illustrated in FIG. 5 can be used alone or in combination with other parts to improve the operation of the de-jitter buffer. At block 500, sector loading, signal quality, or signal quality change may be measured. Based on these measurements, or any combination thereof, the approximate delay of the arriving packets in the signal within that sector is estimated. Next, at block 502, an appropriate de-jitter buffer size is calculated. For example, if the packet arrival delay is estimated to be small, the de-jitter buffer size may be small. On the other hand, if the packet arrival delay is estimated to be large, the de-jitter buffer size may need to be increased. At block 504, the de-jitter buffer is initialized according to the estimated packet delay based on various channel conditions.

  After initialization, the operation of the de-jitter buffer can be adapted according to certain events that can occur during transmission of the message. For example, if the signal quality changes, packet jitter may increase because the sector load increases or the subscriber station moves away from the base station. The de-jitter buffer size can be adapted before this increase occurs. At block 506, a change in signal quality may be detected. Then, at block 508, the steady state operation of the de-jitter buffer is adjusted by increasing or decreasing the de-jitter buffer size according to the signal quality change. For example, as signal quality increases, de-jitter buffer size can be reduced because less jitter can be expected. On the other hand, if the signal quality is degraded, an increase in jitter can be expected, and therefore the de-jitter buffer size can be increased.

  As explained above, another event that causes a change in packet delay is a handoff. At block 510, a handoff may be expected by scheduling an event. For example, a subscriber station may schedule a handoff and may provide scheduling information for a de-jitter buffer that expects the handoff. At block 512, the de-jitter buffer may be adjusted to accommodate for a handoff that is likely to occur. Specifically, the de-jitter buffer increases in size to effectively handle the increased jitter experienced when handoff occurs. Adjusting the de-jitter buffer in block 512 may also include reducing the de-jitter buffer size after handoff if low jitter is expected again.

  Of course, after initialization, it should be understood that the adaptation procedures illustrated in FIG. 5 are performed in any order and are not limited to the exact order shown. For example, a handoff may occur before the signal condition changes. In that case, the de-jitter buffer size may be adapted to accommodate the handoff before adjusting the de-jitter buffer size in response to changes in signal quality.

  Thus, a novel and improved method and apparatus for removing jitter from wireless communications has been disclosed. Data, instructions, instructions, information, signals, bits, symbols, and chips cited throughout the above description advantageously include voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, Alternatively, those skilled in the art will understand that they can be expressed by any combination thereof. Those skilled in the art may further understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein are electronic hardware, computer software, or It will be understood that it is realized as a combination. Various illustrated components, blocks, modules, circuits, and steps have been generally described in terms of their functionality. Whether these functions are implemented as hardware or software depends on specific applications and design constraints imposed on the entire system. The skilled engineer recognizes that, under these circumstances, hardware and software are interchangeable and are best suited to implement the functions described for each particular application. By way of example, the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein can be a digital signal processor (DSP), an application specific integrated circuit (ASIC), Field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components such as registers and FIFOs, processors that execute a set of firmware instructions, any conventional programmable software modules and processors Or any combination of the above designed to implement the functions described above. The processor may advantageously use a microprocessor, but may alternatively use prior art processors, controllers, microcontrollers, programmable logic devices, arrays of logic elements, or state machines. is there. The software modules may be stored in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or other types of storage media known in the art. A typical processor is advantageously connected to the storage medium so that information can be read from and written to it. In the alternative, the storage medium may be integral to the processor. The processor and storage medium can reside in the ASIC. The ASIC can also reside in a telephone or other user terminal. In the alternative, the processor and the storage medium may reside in a telephone or other user terminal. The processor can be realized as a combination of a DSP and a microprocessor, or as two microprocessors cooperating with a DSP core or the like.

  Illustrative embodiments of the present invention have thus been shown and described. However, it will be apparent to those skilled in the art that many modifications can be made to the embodiments disclosed herein without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except as according to the appended claims.

FIG. 1 illustrates a wireless communication system. FIG. 2 is a wireless communication system that supports high data rate (HDR) transmission. FIG. 3 is a block diagram illustrating the basic subsystems of a typical wireless communication system. FIG. 4 is a block diagram illustrating the basic subsystem of a typical subscriber station. FIG. 5 is a flowchart illustrating an exemplary de-jitter buffer process.

Claims (27)

A method of adapting a de-jitter buffer,
Detecting changes in the characteristics of the air link;
Estimating a packet delay based on a change in the characteristic;
Adapting the de-jitter buffer based on the estimated packet delay before a change in the characteristic affects packet arrival time .   The method of claim 1, wherein the characteristic is a measure of sector load.   The method of claim 1, wherein the characteristic is measured signal quality.   4. The method of claim 3, wherein the characteristic is a change in the signal quality.   The method of claim 1, wherein the estimated packet delay is an increase in packet delay and the de-jitter buffer is adapted by increasing its size.   The method of claim 1, wherein the estimated packet delay includes a decrease in packet delay, and the de-jitter buffer is adapted by reducing its size. A method of adapting a de-jitter buffer before a handoff event,
Scheduling the handoff event;
Estimating a packet delay based on the scheduled handoff event;
Adapting the de-jitter buffer based on the estimated packet delay.   The method of claim 7, wherein the de-jitter buffer is adapted by increasing its size.   The method of claim 1, wherein adapting the de-jitter buffer comprises initializing the de-jitter buffer based on the estimated packet delay.   The method of claim 9, wherein the de-jitter buffer is initialized to a size calculated as a function of the estimated packet delay. A receiver configured to receive communication signals over a wireless air link;
Obtain measurements of air link characteristics, estimate packet delay based on changes in the air link characteristics, and dejitter buffer size is adapted before changes in the air link characteristics affect packet arrival times A processor configured to calculate the de-jitter buffer size based on the estimated packet delay ;
A subscriber station comprising a de-jitter buffer configured to have an adaptive size that can match the calculated de-jitter buffer size.   12. The subscriber station of claim 11, wherein the processor is further configured to calculate the de-jitter buffer as a function of sector load.   12. The subscriber station of claim 11, wherein the processor is further configured to calculate the de-jitter buffer size as a function of signal quality.   14. The subscriber station of claim 13, wherein the processor is further configured to calculate the de-jitter buffer size as a function of the signal quality change. A processor configured to obtain information about a scheduled handoff, estimate a packet delay as a function of the scheduled handoff, and calculate a de-jitter buffer size as a function of the estimated packet delay;
With a de-jitter buffer configured to have an adaptable size,
The de-jitter buffer is a subscriber station that can match the calculated size. A computer readable medium incorporating a program of instructions executable by a computer to perform a method of adapting a de-jitter buffer, the method comprising:
Detecting changes in the characteristics of the air link;
Estimating a packet delay based on a change in the characteristic;
Adapting the de-jitter buffer based on the estimated packet delay before a change in the characteristic affects packet arrival time . A computer readable medium incorporating a program of instructions executable by a computer to perform a method of adapting a de-jitter buffer prior to a handoff event, the method comprising:
Scheduling the handoff event;
Estimating a packet delay based on the scheduled handoff event;
Adapting the jitter buffer based on the estimated packet delay. Means for receiving a communication signal over a wireless air link;
Means for determining detection of a change in the characteristics of the wireless air link based on the received communication signal;
Means for calculating a de-jitter buffer size as a function of characteristics determined in the wireless air link;
Means for adapting the de-jitter buffer size before a change in the characteristics of the radio air link affects packet arrival time so that the de-jitter buffer size matches the calculated size Bureau. Means for obtaining information about scheduled handoffs;
Means for estimating packet delay as a function of the scheduled handoff;
Means for calculating a de-jitter buffer size as a function of the estimated packet delay;
Means for matching a de-jitter buffer to said calculated size. Means for detecting changes in the characteristics of the air link;
Means for estimating packet delay based on a change in said characteristic;
Means for storing packets;
Means for storing a delay corresponding to each data packet;
Means for adjusting a size of a de-jitter buffer before a change in the characteristic affects a packet arrival time .   21. The apparatus of claim 20, wherein the means for adjusting incorporates a time warp.   The apparatus of claim 21, wherein the time warp is a function of a received data rate.   21. The apparatus of claim 20, adapted to process voice over internet protocol (VoIP) data.   21. The apparatus of claim 20, wherein the quality of the received signal is a function of sector load in a wireless communication system.   25. The apparatus of claim 24, wherein the quality of the received signal is a function of reverse activity bits.   The apparatus of claim 24, wherein the quality of the received signal is a function of a traffic channel effective bit.   21. The apparatus of claim 20, adapted to adjust a size of the de-jitter buffer in anticipation of handoff.

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